1. You must count calories.
You've heard it before, but because too many people still don't know how many calories are packed into what they eat, this time-tested strategy is Jillian's number-one piece of advice. "Not counting calories is the biggest mistake people make," she says. "Use whatever medium you're on most frequently: the Web — the free site, caloriesperhour.com, is a great resource. Or use an iPhone app. Or carry a pocket calorie counter with you." Find a way.

2. You must avoid processed foods at all costs.
"Processed foods are loaded with preservatives and chemicals — in other words, poison. The right quality food makes such a difference in how you feel. It'll give you strength, make you healthy. I always say, if it had a mother or came from the ground, that's a green-light food. A Cheeto or Ding Dong, don't eat it! If it says high-fructose corn syrup or hydrogenated anything or artificial coloring or sweetener, stay away!"

3. You must do five intense 30-minute workouts a week.
"Thirty minutes is me being kind!" Jillian insists — and she'd rather you didn't break up those 30 minutes into shorter blocks (though, for our money, some exercise is better than none at all). "I would really like to see you do it in one shot. But make it fun. Go walking with friends; plan a family outing. And if it requires you to get up a little earlier, do it, for God's sake!"

4. You must inspire yourself.
"You have to establish the why: Why do you want to change your life? What's inspiring and motivating you? A long life? To wear your skinny jeans to your 10-year high school reunion? That why is gonna carry you through."